265 vs. 285 with 3.73 gears

MN Z-71 · February 22, 2004

Currently I have 265's on 16x8 wheels. 3.73 rear end. Would I notice a big difference by going to 285's? I dont want to go any bigger, or my snow traction will be affected too much.

Thoughts on the 285's?

Wingnut · February 22, 2004

I have two trucks with 285's on them and 3:73s. You lose a little bottom end, but I didn't notice it after a week.

Of course, if you lose a little (low-end) torque....You would probably do better in the snow.

MN Z-71 · February 22, 2004

How about out on the highway...does it downshift more easily on hills? Also how will it affect my speedometer/odometer?

Shotgun · February 22, 2004

Your speedo will be about 6 MPH off.I had put 305's on my 97 Z and really didn't notice the downshifting on hills or anything and I pulled my travel trailer fine.

sdtahoe · February 22, 2004

Same here.. I had 285 Mtr/s on a '90 GMC regular cab long box that originally came with P225/75-16's

Soon after I got it I went with 265's and then moved up to 285's, had no problems with shifting or low end power, I had 3.73's and could light up a back tire whenever I wanted. I did not have my speedometer recalibrated so I had to do some math while driving (off about 13% if I remeber right).

All of this was on the stock rims (16x6.5?) and I had minimal rubbing of the side bites on the tire to the lower a-arm at full turn while backing up. With aftermarket wheels be careful of your backspacing as it may cause some rubbing.

mdub · February 22, 2004

MN Z-71,

The speedometer error depends on your factory calibration. If your truck is calibrated for 265/75/16, the error will be low by 1.9 mph @ 60 (3.2%). With that said, my truck is calibrated for 265s and I'm running 285s, and I've found the error to be almost negligible. I've noticed the friendly "radar reminders" that the local police place along the side of the roads to be real close to my speedometer. Unfortunately, the local state patrol has also caught me a few times to confirm my speedometer accuracy...

If your truck is calibrated for 245/75/16, the error is toward the low side by 4.3 mph @ 60 (7.2%). If this is the case, you might consider having a dealer recalibrate to 265s. As you may know, they can't calibrate any higher than 265s.

Here's a good link for checking speedometer error (once at the site, click 'speedometer check'):

http://www.4lo.com/

Here's a good link for determining tyical tire diameter of A/T tires:

http://www.bfgoodrichtires.com/assets/pdf/...rrain_ta_kd.pdf

-Mdub

MN Z-71 · February 22, 2004

Thanks for the info guys.

Arent all Z-71's calibrated for 265's? Thats what came on the truck stock.

I have 16x8 Eagle 589's, if I remember correctly they have a 4.5" backspacing with a -11mm offset. Anybody have info on whether I will have any rubbing issues on the A-arm?

SilveradoWV · February 22, 2004

My truck came with 245s and not long after I got it I put on 265s. Then I just got a GPS for Christmas and the speedo on the truck matches the GPS EXACTLY. So either 245 to 265 has no effect on the speedo or my truck came programed for 265s.

gmcjoe · February 23, 2004

Arent all Z-71's calibrated for 265's? Thats what came on the truck stock.

Nope, 265s were the optional tire

I went from 265s to 285s with a 3.73 and really noticed a difference in performance down low...

99-2door · February 23, 2004

Thanks for the info guys.

Arent all Z-71's calibrated for 265's? Thats what came on the truck stock.

I have 16x8 Eagle 589's, if I remember correctly they have a 4.5" backspacing with a -11mm offset. Anybody have info on whether I will have any rubbing issues on the A-arm?

I have 16x8s with -11mm and 285s, no rubbing. I did have to trim the front valance a little.

IF your 95 has a Z-71 code it originally had 265/70/r16s. In order to equip the z71 option the truck had to have 265s those years. There is a code for that too, and the sticker on the door should say what size they were.

scooter70 · February 23, 2004

285s and 3.73s here.... yeah, you lose a little bit, but not enough that I thought that the truck was alot slower. Then again, if I were to drive a truck with 245s and 4.10s and then mine, I bet there would be a noticible difference.